Measuring greenhouse gases in agricultural landscapes

Tuesday 6 Dec 2016

A trial in a paddock at Charles Sturt University (CSU) is assessing how new techniques can lead to more accurate measurements of greenhouse gas emissions in agricultural landscapes.

The pilot project, involving CSU, the University of Wollongong and the Australian Nuclear Science and Technology (ANSTO), has been measuring greenhouse gases, including carbon dioxide, methane and nitrous oxide, in the paddock in Wagga Wagga during the past four months.

In a new approach in the field, the study utilises the measurement of emissions of radon gas, a naturally occurring radioactive gas found in soil and rocks.

"We are measuring the radon and greenhouse gases at the same time on the Charles Sturt University Farm at Wagga Wagga," CSU environmental chemist Dr Julia Howitt said.

"The inclusion of both radon and the trace gases is significant because it allows us to improve our understanding of what the atmosphere is doing and therefore more accurately collect data on the greenhouse gases emissions, especially at night."

Through instruments on a tower in the paddock, the gases are sampled at 10 metres and 2 metres above the soil and then fed into a nearby shed containing equipment from the three organisations including portable greenhouse gas analysers.

Dr Howitt said, "The research is being undertaken in a 'typical' paddock of lucerne and rye grass and grazing sheep.

"The instruments are very sensitive as you can see spikes in the data when the sheep were moved into the paddock and during the recent hay bailing.

"This paddock is being used as the research site not only because it represents a typical large scale agricultural landscape but also because comparable greenhouse gas data was collected during research at the same site nearly 20 years ago.

"Therefore we have some existing data to compare the results of this project."

While Dr Howitt is on the ground at CSU in Wagga Wagga, the equipment can be remotely accessed by her co-researchers at the University of Wollongong and ANSTO in Sydney.

"Radon is a radioactive gas that is emitted naturally from the landscape," explained ANSTO's Dr Alastair Williams.

"Because it's chemically unreactive and emitted at a fairly consistent rate from the ground, it can be used as a reliable tracer or yardstick to estimate emissions of greenhouse gases like carbon dioxide, nitrous oxide and methane, which fluctuate more rapidly from place to place and from day to night.

"Radon-based tracer methods are particularly useful when wind speeds are calm during the night, as the more traditional techniques for measuring greenhouse gas emissions perform badly when there is very little atmospheric turbulence present.

"We measure radon in air using a dual flow loop two filter radon detector. These instruments are designed, developed and built by ANSTO, and recognised internationally as being the best of their kind, due to their extremely high sensitivity and accuracy. As radon in the atmosphere exists at ultra-low
concentrations, it can only be measured using nuclear techniques by virtue of its radioactivity," Dr Williams said.

Dr Howitt and some of her co-researchers will be available for interview
at the research site on the University Farm, Agricultural Avenue, CSU in Wagga
Wagga on Tuesday morning 6 December. Contact
CSU Media.